The United States and Britain agree to maintain tough sanctions on Russia over its actions in Ukraine, President Barack Obama said Friday.

"We agree on the need to maintain strong sanctions against Russia until it ends its aggression in Ukraine and on the need to support Ukraine as it implements important economic and democratic reforms," Obama said during a joint press conference with British Prime Minister David Cameron.

Western powers have slapped stringent sanctions on Russia for its actions in eastern Ukraine last year which effectively led to the annexation of Crimea.

Obama has said the sanctions have worked, weakening President Vladimir Putin.

Economic indicators show Russia is sliding toward recession, a sharp reversal of fortune for Putin who is contending with the first shrinkage in his nation's economy since 2009.

The ruble has slumped by 40 percent this year, mostly due to crude oil prices falling by half in the past six months.